A medical image capturing apparatus such as an X-ray computed tomography (CT) apparatus, a magnetic resonance imaging (MRI) apparatus or the like is used to capture time-series images of a subject to which a contrast agent has been administered to obtain information about the hemodynamics of tissue by analyzing the images. This is called perfusion analysis, which uses the fact that the concentration of the contrast agent in the tissue can be obtained from the value of a pixel corresponding to the tissue in the image.
The time-series images of the subject having been administered a contrast agent are captured by, for example, securing the position of the bed of the apparatus and repeatedly capturing the image of a predetermined area at regular intervals. For example, when the medical image capturing apparatus captures an image 60 times at intervals of 1 second, time-series images of one minute consisting of 60 frames are obtained for the area. The medical imaging analyzer performs the perfusion analysis of the time-series images obtained in this way.
In capturing a large organ such as lung, brain, liver, or the like, the image of an area including the whole organ may not sometimes be captured. Like this, if the organ is larger than the available imaging area per one capturing, a contrast agent is administered to a part of the area of the organ to capture time-series images of the area. This is repeated by moving the bed and securing it again. In other words, a contrast agent is administered more than once, and capturing is performed by moving the imaging area to capture the entire area of the organ in divided areas. The images may be captured such that some areas have an overlapping area.
The breathing or body movement of the subject that occurs during scanning or the movement of the bed may cause a difference in either the shape or size or both of the organ to be rendered in time-series images between one and another of the time-series images. This produces a step in the organ of the subject rendered in the entire image obtained by combining the areas. Incidentally, in general, it takes a long time to capture images for perfusion analysis. As a result, in images captured for perfusion analysis, a large difference is likely to occur in the shape of the organ rendered in the images due to the breathing or body movement during the entire capturing time.
As described above, in the perfusion analysis, the transition is analyzed in the pixel value representing the concentration of a contrast agent administered to capture time-series images. However, when time-series images are captured by moving the imaging area with two or more doses of a contrast agent, the contrast agent administered previous to a particular time-series image may remain in the area represented in the time-series images. The contrast agent administered in the past may also be recirculated and represented in the time-series images. In this case, transition occurs in the concentration of the contrast agent administered to capture the time-series image and that of the contrast agent administered previous to the capturing, and thus the transition of a pixel value representing the sum of the concentrations is analyzed. This reduces the accuracy of the perfusion analysis.
The perfusion analysis requires transition information on the pixel value with respect to an artery to be analyzed. However, in an image captured by capturing divided areas, an artery area may sometimes be specified in only a part of partial image areas. In this case, the perfusion analysis cannot be performed for organ in the partial image where an artery area is not specified.